The present invention generally relates to monitoring and controlling semiconductor processing. In particular, the present invention relates to a system and method for optimizing oxidation of an antireflective coating layer via a x-ray reflectometry system.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities, there has been and continues to be efforts toward scaling down device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller feature sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as comers and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with radiation sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular patter. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Present techniques in optical projection printing can resolve images of submicron when photoresists with good linewidth control are used. However, reflection of light from substrate/resist interfaces may produce variations in light intensity scattering of light in the resist during exposure, resulting in non-uniform photoresist linewidth development. Constructive and destructive interference resulting from reflected light is particularly significant when monochromatic or quasi-monochromatic light is used for photoresist exposure. In such cases, the reflected light interferes with the incident light to form standing waves within the resist. In the case of highly reflective substrate regions, the problem is exacerbated since large amplitude standing waves create thin layers of underexposed resist at the wave minima. The underexposed layers can prevent complete resist development causing edge acuity problems in the resist profile.
Antireflective coatings are known and used to mitigate the aforementioned problems. However, the antireflective coatings (ARC) layers are insufficient when used in connection with a Deep Ultra-Violet (DUV) photoresist due to acid formation in the resist when exposed. Therefore, when utilizing a DUV resist, the top portions of the ARC layer can be oxidized to mitigate footing of the patterned features after development of the resist layer. However, the thickness of the oxidized ARC layer is critical. Insufficient oxidation may result in problems with critical dimension control, which results in costly repair, fabrication delays and product yield losses. Therefore, there is an unmet need for a system and method for determining and controlling the appropriate oxidation of an ARC layer during a photoresist process.
The present invention relates to a system and method for providing in-situ thickness and process monitoring to help achieve a desired thickness of an oxidized ARC portion disposed over an ARC layer. The system and method may be employed to monitor the oxidized ARC portion during growth as well as during processing of the oxidized ARC layer. During semiconductor processing, a photoresist layer (e.g., DUV resist) may be deposited over the oxidized ARC layer for patterning. However, removal of the photoresist layer can damage the underlying oxidized ARC or ARC layer, resulting in diminished CD control and ultimately, poor device performance. Therefore, by monitoring the thickness of the oxidized portion of the ARC layer during semiconductor processing, one or more process control parameters may be adjusted to help achieve a desired oxidized portion thickness. As a result, the number of process steps required to achieve the desired oxidized portion thickness may be reduced, providing a more efficient and economical process.
Alternatively, the system and method according to the present invention may be employed in a closed-loop system with feedback control for optimizing ARC and oxidized ARC thickness while mitigating defective device formation and wafer yield loss. For example, the system and method may detect and assess the thickness of the ARC and/or oxidized ARC layer to determine an amount of oxidized ARC layer lost or damaged. The actual thickness may then be compared to a desired or preferred thickness. According to these measurements, the oxidized ARC layer may then undergo further processing to repair the current and/or subsequent wafer to mitigate recurring defects.
One aspect of the present invention provides a semiconductor processing system. The system includes a processing chamber operable to form an oxidized ARC layer or portion over an ARC layer on a substrate located in the chamber. An x-ray scattering/reflectometry system performs in-situ thickness measurements of the oxidized portion being formed and provides a measurement signal indicative of the measured thickness. In accordance with another aspect of the present invention, the thickness of the ARC layer may also be monitored and controlled. A signature is then generated utilizing the measurement signal and the signature is compared with a library of signatures to determine the thickness of the oxidized portion.
Yet another aspect of the present invention provides a method to facilitate formation of an oxidized portion of an ARC layer on a substrate. The method includes forming an oxidized portion of an ARC over an ARC layer disposed on the substrate. An x-ray beam is directed at the oxidized portion and a measurement signal is generated based-on the reflected (scattered) portion of the x-ray beam. The thickness of the oxidized portion is then determined based on the measurement signal while the oxidized portion is being formed at the substrate.